Ferromagnetic materials



FERROMAGNETIC MATERIALSv No Drawing. Application January 29, 1953, I Serial No. 334,075

Claims priority, application Great Britain February 22, 1952 4 Claims. (Cl. 252-625) This invention relates to magnetic materials of the kind generally known as mixed ferrites. A ferrite consists of a ferromagnetic spinel type material of the general formula XOFezOs Where X is a divalent metal. A mixed ferrite consists of a solid solution of two or more such ferrites.

In British Patent 683,722 to D. H. Owen, published December 3, 1952, there has been proposed a process for manufacturing a ferro-magnetic spinel type heterogeneous material consisting of mixed oxides with the addition of a small proportion of either kaolin, silica or kieselguhr which mixture is subjected to a heat treatment at a temperature lying between 1000" C. and 1400 C.

It is an aim of the present invention to provide a ferrite which can be produced with consistent electrical properties at a lower temperature than was previously required.

According to the invention there is provided a magnetic material comprising a mixture of oxides, which themselves combine to form a ferrite, and a low melting point silicate of one of the metals whose oxide forms the ferrite.

The mixture may be, for example, of manganese oxide MnO, zinc oxide ZnO, and ferric oxide FezOs to which is added either ferrous silicate, manganese silicate, ferrous manganese silicate or all three. In the case of a mixture of nickel oxide NiO, zinc oxide ZnO, and ferric oxide F6203 there is added either ferrous silicate or nickel silicate or both. These additives are all low melting point silicates, which improve the ease of sintering of the material and assist in producing a more consistently reproducible result than is normal for the known ferrites.

By low melting point silicate is meant a silicate whos melting point is in the region of 1100" C.

In addition a core may be assembled of magnetic materials, made according to the invention, which have temperature coeflicients of permeability of opposite sign so that the complete core displays a very low temperature coefficient.

A description will now be given of the preparation and electrical properties of mixtures according to the invention.

The mixtures comprise oxides in the following proportions:

25 molar percent MnO 25 molar percent ZnO 50 molar percent FezOa together with the addition of ferrous silicate in varying proportions.

The mixtures were all ball milled for 20 hours, pressed at a pressure of 25 tons per square inch, and heat treated for 6 hours at 1150 C. in an atmosphere of commercial nitrogen gas.

The oxides were derived from technical grades of the appropriate oxalates by the decomposition of the oxalates. The electrical properties of various mixtures according to the invention together with those of known mixtures are as follows:

United States. Patent MIXTURES ACCORDING TO THE INVENTION Percent Ferrous Heat Treatment K1 K: K,

Silicate By Weight l,150 C. for 6 hrs 1 8 1,150 C. for 6 hrs 3 2 1,150 0. for 6 his"--. gig 5% 3 8 1,150 0. for 6 hrs KNOWN MIXTURES 6 it? a: a: 1

a as 5 No Ferrous Slli- 0 Gate present 1,250 o. for 6 hrs g 5 where a is the permeability, K1 is the residual loss, K2 is the hysteresis loss, and Ke is the eddy current loss of the material.

From these results it can be seen that a considerable control may be exercised over the properties of the mixture and the consistency of reproduction by the addition of varying amounts of silicate, and that for the same heat treatment greatly improved permeability and reduced losses result over those obtained without the silicate.

In order to obtain a core with a low temperature coefiicient of permeability a core may be constructed comprising a number of sections each having a different temperature coefficient. For example if a core is composed of four sections from two mixtures which have positive and negative coefiicients, the size and number of sections having a positive coeflicient can be so arranged with the sections having a negative coeflicient that the overall coeflicient of the core is very small in practice viz., less than :45 parts per million per degree C. over a temperature range of from 15 C. to 45 C.

The following properties were measured on two similar sections in the shape of toroidal rings at the permeabilities shown over the temperature range of from 15 C. to 45 C.

The oxide mixture for the sections was prepared in the manner previously described and the first section contained 1% ferrous silicate, while the second section contained no ferrous silicate.

Percent Temp. Goefii- Ferrous Heat Treatp K K2 Kn cient, parts Silicate ment per million by weight per C.

1% 1,150 O. for 668 33. 5 1. 3 .67 11, 400

6 hours. None 1,250 C. for 710 29 2.0 .75 +8, 400

6 hours.

and particular modifications thereof, it isto be clearly understoodthat' this description is made only by way of example and-not as a limitation on the scope of the irrvention.

What we claim is:

1. A sintered ferromagnetic material of the spinel' type consisting essentially of a mixture of approximately 50 mole per cent FezOs, 25 mole per cent M110. and. 25 mole per cent 2110, together with the addition of a silicate selected from the group consisting of manganous silicate, and ferrous silicate, said silicate being present in an amount between 1 and 6.6 per cent by Weight of said mixture of oxides and havinga melting point in the regionv of 11001 C.

2. A ferromagnetic, material according to claim 1 wherein said silicate is a ferrous'silicate.

3. A ferromagnetic material according to claim 1 wherein said-silicate is a ferrous silicate in an amount of approximately 1 percent by weight of the oxide mixture.

References Cited in the file of this patent UNITED STATES PATENTS Snoek et a1 May 8, 1951 Albers-Sch'oenberg Aug. 21, 1951 OTHER REFERENCES Langes Handbook of Chemistry, 4th Ed., page 154, 1941.

Mellor: A Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 6, page 905. 

1. A SINTERED FERROMAGNETIC MATERIAL OF THE SPINEL TYPE CONSISTING ESSENTIALLY OF A MIXTURE OF APPROXIMATELY 50 MOLE PER CENT FE2O3, 25 MOLE PER CENT MNO AND 25 MOLE PER CENT ZNO, TOGETHER WITH THE ADDITION OF A SILICATE SELECTED FROM THE GROUP CONSISTING OF MANGANOUS SILICATE, AND FERROUS SILICATE, SAID SILICATE BEING PRESENT IN AN AMOUNT BETWEEN 1 AND 6.6 PER CENT BY WEIGHT OF SAID MIXTURE OF OXIDES AND HAVING A MELTING POINT IN THE REGION OF 1100* C. 